Eddy current array technology is a widely used for quality control testing on objects such as wire, rods or tubes. This testing often involves having the test objects travel along a work path, passing through eddy current probe(s).
Eddy current testing (as opposed to eddy current array testing) can be performed on discs and other shaped objects constructed of conductive and/or non-magnetic materials to look for defects and wear. Eddy current testing may use eddy current coils designed to generate a changing magnetic field that may interact with the disc to generate an eddy current. Variations in the phase and magnitude of the generated eddy current may be measured by measuring changes to the current flowing in the coil. Alternatively, changes in phase and magnitude of the generated eddy current may be measured using a second coil. Changes in the phase and magnitude of the generated eddy current may indicate one or more flaws in the discs, such as small cracks that may lead to failures if not addressed. While eddy current inspection methods may provide equivalent sensitivity to magnetic particle inspection methods, current eddy current inspection methods are limited to single small element and rigid array probes. Due to their small size and rigidity, such probes make inspection of large discs and other large components that have varying and multiple geometries difficult and time-consuming, and therefore expensive.
Eddy current sensor arrays have been employed to measure stress on airplane parts, for example, on the landing gear, and to measure weights of components. For example, U.S. Pat. No. 8,237,433 discloses methods for monitoring of stresses and other material properties. These methods use measurements of effective electrical properties, such as magnetic permeability and electrical conductivity, to infer the state of the test material, such as the stress, temperature, or overload condition. The sensors, which can be single element sensors or sensor arrays, can be used to periodically inspect selected locations, mounted to the test material, or scanned over the test material to generate two-dimensional images of the material properties. Magnetic field or eddy current based inductive and giant magnetoresistive sensors may be used on magnetizable and/or conducting materials, while capacitive sensors can be used for dielectric materials. Methods are also described for the use of state-sensitive layers to determine the state of materials of interest. These methods allow the weight of articles, such as aircraft, to be determined. The probes in use would not be suitable for assessing wear and identifying surface defects in wheels and rims in remote locations, nor would they be suitable for use on abrasive surfaces, as could occur on a wheel or rim.
Eddy current arrays can also be used in production and inspection lines. For example, U.S. Pat. No. 8,264,221 discloses an eddy current probe assembly suitable for inspecting a test object with longitudinal shape, being passed through the assembly in the object's axial direction during an inspection session, the probe assembly comprising multiple probe modules being disposed in a radial plane and with the modules partially overlaying on each other forming an IRIS structure encircling an inspection zone, wherein a movement in unison of each of the probe modules closer to or further away from the center of the inspection zone makes the inspection zone enlarged or contracted. Spring tension is applied on each of the probe modules so that constant life-off in maintained between the probe modules and the test surface. Array of eddy current elements for each probe module and multiple layers of probe modules can be employed to achieve complete coverage of the test surface. The radial cross-sectional shapes of the test objects can be of round or polygonal. This design is suitable for inspection lines in production facilities and would not be suitable for assessing surface discontinuities and wear in off road vehicle rims and wheels.
Flexible probes that are strap-like have been disclosed. These can be pressed into round-edged shapes, for example, pipeline, tube inspection, and aircraft. However, they are only useful for assessing wear and integrity of smooth surfaces and are subject to wear if used on hard edges or rough surfaces.
A patent pending flexible probe array (FPA) configured in a glove that can be worn by an inspector has been disclosed. The FPA conforms to the inspection surface and allows inspection of a wide region with each scan of the array. With this arrangement, the operator receives tactile feedback of surface profile changes and is able to adjust the pressure on the FPA to accommodate changing geometries. The FPA approach eliminates the need to maintain probe alignment and the raster scanning needed with a conventional probe. The system has been successfully demonstrated at four operating power plants. A major deficiency is that it relies heavily on the proficiency of the user and therefore there is a risk of human error. Further, the results would vary from operator to operator as there is no accurate feedback to the operator to ensure consistency between operators. In addition, the scan coverage on the glove is very small. Still further, the flexible probe would be ill suited for environments where there is dust, dirt and potentially an abrasive test surface.
Current practices for inspecting off road vehicle wheels and rims, particularly in the mining sector, involves shipping wheels and rims to a central facility for inspection, repair and certification. This facility may be hundreds of miles from the mine site. When at the facility, electromagnetic, in particular, Magnetic Particle Inspection is conducted. Approximately 50% of the wheels and rims shipped from a mine site to a central facility are in good condition. The logistics of this is cumbersome but is the only option available to mining customers. Further to this, the assessment is a visual assessment, therefore depending on the skill and experience of the assessor. Still further, the data are not electronically acquired and stored and must, therefore, be manually entered should an archive be desired.
The most critical region for examination on an OTR wheel and rim is where metal meets metal. The sections which have direct contact with the truck and assembly parts are the gutter section, back section, mounting disc (knave) and or mounting taper (rim). The gutter section of an OTR rim or wheel base has 4 distinct individual groove patterns (HDT, EM, EMH, & EV). The groove design is usually selected based on rim size and application. The back section has 3 distinct manufacture designs (Standard/MES, TSR & IGLR/Wedge). Selection of the back section design is related to tire support and positioning on the truck. Significantly, there are seven main rim profiles used in OTR mining truck vehicles. There are also various wheel and rim profiles for graders, loaders, logging trucks and other off road vehicles.
What is needed therefore is a probe and method suited to field testing to accurately and quickly identify defects and wear. The method would preferably not rely on visual inspection. It would be preferable if the probe allowed for a quantitative measure of wear and it there was a standard and method for assessing pass/fail using such probe. It would be further preferably if only defects of significance to the certification of the wheels and rims of off road vehicles were identified. It would be of further advantage if wear on the probe could be reduced, and if probe life could be extended. It would be advantageous if the resulting data were sent directly to a computer, analyzed, displayed in three dimensions and archived. It would be of a still greater advantage if the data could be used to develop predictive models for subsequent scheduling of testing.